The immune system comprises both the innate immune system and the adaptive, or acquired immune system. Many host cells participate in the processes of innate and adaptive immunity, such as neutrophils, T- and B-lymphocytes, macrophages and monocytes, dendritic cells, and plasma cells. They usually act in concert, affecting one another, particularly in the regulation of certain factors and cytokines that contribute to the recognition and processing of innate and external noxients, and these systems have evolved over the millions of years of the development of vertebrate, mammalian, and human organisms.
A major goal of immunotherapy is to exploit or enhance a patient's immune system against an innate or foreign noxient, such as a malignant cell or an invading microorganism. The immune system has been studied more in relation to recognizing and responding to exogenous noxients, such as microbial organisms, than it has in relation to indigenous malfunctions, such as cancer and certain autoimmune and immune-dysregulatory diseases, particularly since the latter may have both genetic as well as environmental components. The defenses against microbial organisms, such as bacteria, fungi, parasites, and viruses, are innate to the particular organism, with the immune system being programmed to recognize biochemical patterns of these microorganisms and to respond to attack them without requiring prior exposure to the microorganism. This innate immune system includes, for example, neutrophils, natural killer cells and monocytes/macrophages that can eradicate the invading microorganisms by direct engulfment and destruction.
The innate immune response is often referred to as a nonspecific one that controls an invading external noxient until the more specific adaptive immune system can marshal specific antibodies and T cells (cf. Modlin et al., N Engl J Med 1999, 340:1834-1835; Das, Crit. Care 2000; 4:290-296). The nonspecific immune responses involve the lymphatic system and phagocytes. The lymphatic system includes the lymphocytes and macrophages. Macrophages can engulf, kill and dispose of foreign particles. Phagocytes include neutrophils and macrophages, which again ingest, degrade and dispose of debris, and have receptors for complement and antibody. In summary, the innate immune system provides a line of defense again certain antigens because of inherited characteristics.
In contrast, the adaptive, or acquired, immune system, is highly evolved and very specific in its responses. It is called an adaptive system because is occurs during the lifetime of an individual as an adaptation to infection with a pathogen. Adaptive immunity can be artificially acquired in response to a vaccine (antigens) or by administering antibodies, or can be naturally acquired by infection. The acquired immunity can be active, if an antibody was produced, or it can be passive, if exogenous antibody made form another source is injected.
The adaptive immune system produces antibodies specific to a given antigen. The simplest and most direct way in which antibodies provide protection is by binding to them and thereby blocking their access to cells that they may infect or destroy. This is known as neutralization. Binding by antibodies, however, is not sufficient to arrest the replication of bacteria that multiply outside cells. In this case, one role of antibody is to enable a phagocytic cell to ingest and destroy the bacterium. This is known as opsonization. The third function of antibodies is to activate a system of plasma proteins, known as complement. In many cases, the adaptive immune system confers lifelong protective immunity to re-infection with the same pathogen, because the adaptive immune system has a ‘memory’ of the antigens presented to it.
Antibody-mediated immunity is called humoral immunity and is regulated by B cells and the antibodies they produce. Cell-mediated immunity is controlled by T cells. Both humoral and cell-mediated immunity participate in protecting the host from invading organisms. This interplay can result in an effective killing or control of foreign organisms. Occasionally, however, the interplay can become erratic. In these cases, there is a dysregulation that can cause disease. Sometimes the disease is life-threatening, such as with septic shock and certain autoimmune disorders.
The B and T lymphocytes are critical components of a specific immune response. B cells are activated by antigen to engender clones of antigen-specific cells that mediate adaptive immunity. Most clones differentiate to plasma cells that secrete antibody, while a few clones form memory cells that revert to plasma cells. Upon subsequent re-infection, memory cells produce a higher level of antibody in a shorter period than in the primary response. Antibodies secreted by the plasma cells can play multiple roles in immunity, such as binding and neutralizing a foreign agent, acting as opsonins (IgG) to promote phagocytosis, directly affecting metabolism and growth of some organisms, engaging in antigen-antibody reactions that activate complement, causing phagocytosis and membrane attack complex, and/or engaging in antigen-antibody reactions that activate T cells and other killer cells.
T lymphocytes function as both helper cells and suppressor cells. Helper T cells induce antigen-specific B cells and effector T cells to proliferate and differentiate. Suppressor T cells interact with helper T cells to prevent an immune response or to suppress an ongoing one, or to regulate effector T cells. Cytotoxic T cells destroy antigen by binding to target cells. In a delayed-type hypersensitivity reaction, the T cells do not destroy antigen, but attract macrophages, neutrophils and other cells to destroy and dispose of the antigen.
T cells can detect the presence of intracellular pathogens because infected cells display on their surface peptide fragments derived from the pathogens' proteins. These foreign peptides are delivered to the cell surface by specialized host-cell glycoproteins, termed Major Histocompatibility Complex (MHC) molecules. The recognition of antigen as a small peptide fragment bound to a MHC molecule and displayed at the cell surface is one of the most distinctive features of T cells. There are two different classes of MHC molecules, know as MHC class I and MHC class II, that deliver peptides from different cellular compartments to the surface of the infected cell. Peptides from the cytosol are bound to MHC class I molecules which are expressed on the majority of nucleated cells and are recognized by CD8+ T cells. MHC class II molecules, in contrast, traffic to lysosomes for sampling endocytosed protein antigens which are presented to the CD4+ T cells (Bryant and Ploegh, Curr Opin Immunol 2004; 16:96-102).
CD8+ T cells differentiate into cytotoxic T cells, and kill the cell. CD4+ T cells differentiate into two types of effector T cells. Pathogens that accumulate in large numbers inside macrophage vesicles tend to stimulate the differentiation of TH1 cells which activate macrophages and induce B cells to make IgG antibodies that are effective in opsonizing extracellular pathogens for uptake by phagocytes. Extracellular antigens tend to stimulate the production of TH2 cells which initiate the humoral immune response by activating naive antigen-specific B cells to produce IgM antibodies, inter alia.
The innate and adaptive immune systems interact, in that the cells of the innate immune system can express various molecules that can interact with or trigger the adaptive immune system by activating certain cells capable of producing immune factors, such as by activating T and B cells of the lymphatic series of leukocytes. The early induced but non-adaptive responses are important for two main reasons. First, they can repel a pathogen or, more often, control it until an adaptive immune response can be mounted. Second, these early responses influence the adaptive response in several ways. For example, the innate immune response produces cytokines and other inflammatory mediators that have profound effects on subsequent events, including the recruitment of new phagocytic cells to local sites of infection. Another effect of these mediators is to induce the expression of adhesion molecules on the endothelial cells of the local blood vessels, which bind to the surface of circulating monocytes and neutrophils and greatly increase their rate of migration of these cells out of the blood and into the tissues. These events all are included under the term inflammation, which is a feature of the innate immune system that forms part of the protective response at a localized site to isolate, destroy and remove a foreign material. This is followed by repair. Inflammation is divided into acute and chronic forms.
The immune system communicates via nonspecific tissue resistance factors. These include the interferons, which are proteins produced in response to viruses, endotoxins and certain bacteria. Interferons inhibit viral replication and activate certain host-defense responses. Infected cells produce interferon that binds the infected cells to other, neighboring cells, causing them to produce antiviral proteins and enzymes that interfere with viral gene transcription and proteins synthesis. Interferons can also affect normal cell growth and suppress cell-mediated immunity.
Complement is another nonspecific tissue resistance factor, and comprises plasma proteins and membrane proteins that mediate specific and non-specific defenses. Complement has two pathways, the classical pathway associated with specific defense, and the alternative pathway that is activated in the absence of specific antibody, and is thus non-specific. In the classical pathway, antigen-antibody complexes are recognized when C1 interacts with the Fc of the antibody, such as IgM and to some extent, IgG, ultimately causing mast cells to release chemotactic factors, vascular mediators and a respiratory burst in phagocytes, as one of many mechanisms. The key complement factors include C3a and C5a, which cause mast cells to release chemotactic factors such as histamine and serotonin that attract phagocytes, antibodies and complement, etc. Other key complement factors are C3b and C5b, which enhance phagocytosis of foreign cells, and C8 and C9, which induce lysis of foreign cells (membrane attack complex).
Cancer cells can escape immune surveillance by avoiding complement activation, especially by the expression of membrane-associated complement regulatory proteins, such as CD55 (decay-accelerating factor), CD46 (membrane cofactor protein), and CD59 (protectin), and it is believed that the over-expression of these proteins on cancer cell membranes protects these cancers from complement activation (Brasoveanu et al., Lab Invest 1996; 74:33-42; Jarvis et al., Int J Cancer 1997; 71:1049-1055; Yu et al., Clin Exp Immunol 1999; 115:13-18; Murray et al., Gynecol Oncol 2000; 76:176-182; Donin et al., Clin Exp Immunol 2003; 131:254-263). Attempts have been made, unsuccessfully, to increase the susceptibility to complement-mediated lysis by use of neutralizing antibodies against CD46, CD55 and CD59 (Varsano et al., Clin Exp Immunol 1998; 113:173-182 Junnikkala et al., J Immunol 2000; 164:6075-6081; Maenpaa et al., Am J Pathol 1996; 148:1139-1162; Goiter, Lab Invest 1996; 74:1039-1049. In the latter study, CD46 and CD55 antibodies were, in contrast to CD59 antibodies, ineffective. This suggests that other targets, or the use of antibodies against multiple complement regulatory proteins, or against both complement regulatory proteins and other mediators of immunity may be required. This general failure contradicts the speculation of Fishelson et al. (Mol Immunol 2003: 40:109-123) and the suggestion from other studies that treatment of cancer patients with antibodies to membrane complement regulatory proteins in combination with anticancer complement-fixing antibodies will improve therapeutic efficacy.
Gelderman et al. (Mol Immunol 2003; 40:13-23) reported that membrane-bound complement regulatory proteins (mCRP) inhibit complement activation by an immunotherapeutic mAb in a syngeneic rat colorectal cancer model. While the use of mAb against tumor antigens and mCRP overcame an observed effect of mCRP on tumor cells, there has been no direct evidence to support this approach. Still other attempts to use bispecific antibodies against CD55 and against a tumor antigen (G250 or EpCAM) have been suggested by Gelderman et al. (Lab Invest 2002; 82:483-493; Eur J Immunol 2002; 32:128-135) based on in vitro studies that showed a 2-13-fold increase in C3 deposition compared to use of the parental antitumor antibody. However, no results involving enhanced cell killing were reported. Jurianz et al. (Immunopharmacology 1999; 42:209-218) also suggested that combining treatment of a tumor with anti-HER2 antibodies in vitro could be enhanced by prior treatment with antibody-neutralization of membrane-complement-regulatory protein, but again no in vivo results were provided. Sier et al. (Int J Cancer 2004; 109:900-908) recently reported that a bispecific antibody made against an antigen expressed on renal cell carcinoma (Mab G250) and CD55 enhanced killing of renal cancer cells in spheroids when beta-glucan was added, suggesting that the presence of CR3-priming beta-glucan was obligatory.
Neutrophils, another cell involved in innate immune response, also ingest, degrade and dispose of debris. Neutrophils have receptors for complement and antibody. By means of complement-receptor bridges and antibody, the foreign noxients can be captured and presented to phagocytes for engulfment and killing.
Macrophages are white blood cells that are part of the innate system that continually search for foreign antigenic substances. As part of the innate immune response, macrophages engulf, kill and dispose of foreign particles. However, they also process antigens for presentation to B and T cells, invoking humoral or cell-mediated immune responses.
The dendritic cell is one of the major means by which innate and adaptive immune systems communicate (Reis e Sousa, Curr Opin Immunol 2004; 16:21-25). It is believed that these cells shape the adaptive immune response by the reactions to microbial molecules or signals. Dendritic cells capture, process and present antigens, thus activating CD4+ and CD8+ naive T lymphocytes, leading to the induction of primary immune responses, and derive their stimulatory potency from expression of MHC class I, MHC class II, and accessory molecules, such as CD40, CD54, CD80, CD86, and T-cell activating cytokines (Steinman, J Exp Hematol 1996; 24:859-862; Banchereau and Steinman, Nature 1998; 392:245-252). These properties have made dendritic cells candidates for immunotherapy of cancers and infectious diseases (Nestle, Oncogene 2000; 19:673-679; Fong and Engleman, Annu Rev Immunol 2000; 18:245-273; Lindquist and Pisa, Med Oncol 2002; 19:197-211), and have been shown to induce antigen-specific cytotoxic T cells that result in strong immunity to viruses and tumors (Kono et al., Clin Cancer Res 2002; 8:394-40).
Also important for interaction of the innate and adaptive immune systems is the NK cell, which appears as a lymphocyte but behaves like a part of the innate immune system. NK cells have been implicated in the killing of tumor cells as well as essential in the response to viral infections (Lanier, Curr Opin Immunol 2003; 15:308-314; Carayannopoulos and Yokoyama, Curr Opin Immunol 2004; 16:26-33). Yet another important mechanism of the innate immune system is the activation of cytokine mediators that alert other cells of the mammalian host to the presence of infection, of which a key component is the transcription factor NF-κB (Li and Verna, Nat Rev Immunol 2002; 2:725-734).
As mentioned earlier, the immune system can overreact, resulting in allergies or autoimmune diseases. It can also be suppressed, absent, or destroyed, resulting in disease and death. When the immune system cannot distinguish between “self” and “nonself,” it can attach and destroy cells and tissues of the body, producing autoimmune diseases, e.g., juvenile diabetes, multiple sclerosis, myasthenia gravis, systemic lupus erythematosus, rheumatoid arthritis, and immune thrombocytopenic purpura. Immunodeficiency disease results from the lack or failure of one or more parts of the immune system, and makes the individuals susceptible to diseases that usually do not affect individuals with a normal immune system. Examples of immunodeficiency disease are severe combined immunodeficiency disease (SCID) and acquired immunodeficiency disease (AIDS). The latter results from human immunodeficiency virus (HIV) and the former from enzyme or other inherited defects, such as adenosine deaminase deficiency.
The application of immunotherapy to cancer involves a number of approaches to engage or exploit the immune system, such as adoptive transfer of anti-tumor-reactive T cells and the use of vaccines, as well as breaking tolerance to tumor self-antigens by inhibiting regulatory cells, and boosting T-cell immunity by use of various cytokines and so-called immune-enhancing molecules (Antonia et al., Curr Opin Immunol 2004; 16:130-136). Dendritic-cell vaccines have also been described. Direct and indirect (mediated by host effector cells) actions of antibodies administered to patients by targeting tumor-cell antigens/receptors have now entered the cancer therapy armamentarium, as exemplified by antibodies against CD20 and CD52 in the therapy of lymphomas and leukemia; anti-epidermal growth factor receptor (EGFR), the anti-HER2/neu variant, in the therapy of diverse solid tumors; and anti-vascular endothelium growth factor (VEGF) for the treatment of certain solid tumors. Although active when given alone, most of these show enhanced antitumor effects when combined with other treatment modalities, such as drugs and radiation. Using these tumor-targeting antibodies to deliver cytotoxic drugs or isotopes is still another method of immunotherapy that has entered the clinic. These and other methods of cancer immunotherapy have been reviewed in Huber and Wolfel, J Cancer Res Clin Oncol 2004; 130:367-374. However, at best these approaches show reduction of tumor and improved survival in a proportion of the patients, most of whom eventually relapse, thus requiring other therapeutic interventions and different strategies to control their disease.
Sepsis is a major medical and economic burden to our society, affecting about 700,000 people annually in the United States, causing over 200,000 deaths annually, and costing approximately $16.7 billion per year (Angus et al., Crit Care Med 2001; 29:1303-1310; Martin et al., N Engl J Med 2003; 348:1546-1554). The definition of sepsis has been difficult, and historically it was defined as the systemic host response to an infection. A discussion of the clinical definition of sepsis, encompassing systemic inflammatory response syndrome (SIRS), sepsis per se, severe sepsis, septic shock, and multiple organ dysfunction syndrome (MODS) is contained in Riedmann et al., J Clin Invest 2003; 112:460-467. Since it has been a common belief that sepsis is caused by the host's overwhelming reaction to the invading microorganisms, and that the patient is more endangered by this response that than the invading microorganisms, suppression of the immune and inflammatory responses was an early goal of therapy.
Numerous and diverse methods of immunosuppression or of neutralizing proinflammatory cytokines have proven to be unsuccessful clinically in patients with sepsis and septic shock anti-inflammatory strategies. (Riedmann, et al., cited above; Van Amersfoort et al. (Clin Microbiol Rev 2003; 16:379-414), such as general immunosuppression, use of nonsteroidal anti-inflammatory drugs, TNF-α antibody (infliximab) or a TNF-R:Fc fusion protein (etanercept), IL-1 (interleukin-1) receptor antagonist, or high doses of corticosteroids. However, a success in the treatment of sepsis in adults was the PROWESS study (Human Activated Protein C Worldwide Evaluation in Severe Sepsis (Bernard et al., N Engl J Med 2001; 344:699-709)), showing a lower mortality (24.7%) than in the placebo group (30.8%). This activated protein C (APC) agent probably inhibits both thrombosis and inflammation, whereas fibrinolysis is fostered. Friggeri et al. (2012, Mol Med 18:825-33) reported that APC degrades histones H3 and H4, which block uptake and clearance of apoptotic cells by macrophages and thereby contribute to organ system dysfunction and mortality in acute inflammatory states. Van Amersfoort et al. state, in their review (ibid.) that: “Although the blocking or modulation of a number of other targets including complement and coagulation factors, neutrophil adherence, and NO release, are promising in animals, it remains to be determined whether these therapeutic approaches will be effective in humans.” This is further emphasized in a review by Abraham, “Why immunomodulatory therapies have not worked in sepsis” (Intensive Care Med 1999; 25:556-566). In general, although many rodent models of inflammation and sepsis have shown encouraging results with diverse agents over the past decade or more, most agents translated to the clinic failed to reproduce in humans what was observed in these animal models, so that there remains a need to provide new agents that can control the complex presentations and multiple-organ involvement of various diseases involving sepsis, coagulopathy, and certain neurodegenerative conditions having inflammatory or immune dysregulatory components.
More recent work on immunoglobulins in sepsis or septic shock has been reported. For example, Toussaint and Gerlach (2012, Curr Infect Dis Rep 14:522-29) summarized the use of ivIG as an adjunct therapy in sepsis. The metanalysis failed to show any strong correlation between general immunoglobulin therapy and outcome. LaRosa and Opal (2012, Curr Infect Dis Rep 14:474-83) reported on new therapeutic agents of potential use in sepsis. Among other agents, anti-TNF antibodies are in current clinical trials for sepsis, while complement antagonists have shown promising results in preclinical models of sepsis. Nalesso et al. (2012, Curr Infect Dis Rep 14:462-73) suggested that combination therapies with multiple agents may prove more effective for sepsis treatment. The immunopathogenesis of sepsis has been summarized by Cohen (2002, Nature 420:885-91).
The immune system in sepsis is believed to have an early intense proinflammatory response after infection or trauma, leading to organ damage, but it is also believed that the innate immune system often fails to effectively kill invading microorganisms (Riedmann and Ward, Expert Opin Biol Ther 2003; 3:339-350). There have been some studies of macrophage migration inhibitory factor (MIF) in connection with sepsis that have shown some promise. For example, blockage of MIF or targeted disruption of the MIF gene significantly improved survival in a model of septic shock in mice (Calandra et al., Nature Med 2000; 6:164-170), and several lines of evidence have pointed to MIF as a potential target for therapeutic intervention in septic patients (Riedmann et al., cited above). Bucala et al. (U.S. Pat. No. 6,645,493 B1) have claimed that an anti-MIF antibody can be effective therapeutically for treating a condition or disease caused by cytokine-mediated toxicity, including different forms of sepsis, inflammatory diseases, acute respiratory disease syndrome, granulomatous diseases, chronic infections, transplant rejection, cachexia, asthma, viral infections, parasitic infections, malaria, and bacterial infections, which is incorporated herein in its entirety, including references. The use of anti-LPS (lipopolysaccharide) antibodies alone similarly has had mixed results in the treatment of patients with septic shock (Astiz and Rackow, Lancet 1998; 351:1501-1505; Van Amersfoort et al., Clin Microbiol Rev 2003; 16:379-414.
While both LPS and MIF have been pursued as targets in the treatment of sepsis and septic shock, approaches which target LPS or MIF alone by an antibody have not been sufficient to control the diverse manifestations of sepsis, especially in advanced and severe forms. Similarly, use of cytokines, such as IL-1, IL-6 (interleukin-6), IL-8 (interleukin-8), etc., as targets for antibodies for the treatment of sepsis and other cytokine-mediated toxic reactions, has not proven to be sufficient for a meaningful control of this disease. Therefore, in addition to the need to discover additional targets of the cytokine cascade involved in the endogenous response in sepsis, it has now been discovered that bi- and multi-functional antibodies targeting at least one cytokine or causative agent, such as MIF or lipopolysaccharide (LPS), is advantageous, especially when combined with the binding to a host cell (or its receptor) engaged in the inflammatory or immune response, such as T cells, macrophages or dendritic cells. Antibodies against an MHC class II invariant chain target, such as CD74, have been proposed by Bucala et al. (US 2003/0013122 A1), for treating MIF-regulated diseases, and Hansen et al. (US 2004/0115193 A1) proposed at least one CD74 antibody for treating an immune dysregulation disease, an autoimmune disease, organ graft rejection, and graft-versus-host disease. Hansen et al. describe the use of fusion proteins of anti-CD74 with other antibodies reacting with antigens/receptors on host cells such as lymphocytes and macrophages for the treatment of such diseases. However, combinations with targets other than CD74 are not suggested, and the disclosure focuses on a different method of immunotherapy. Similar targets are also useful to treat atherosclerotic plaques (Burger-Kentischer et al., Circulation 2002; 105:1561-1566).
In the treatment of infectious, autoimmune, organ transplantation, inflammatory, and graft-versus-host (and other immunoregulatory) diseases, diverse and relatively non-specific cytotoxic agents are used to either kill or eliminate the noxient or microorganism, or to depress the host's immune response to a foreign graft or immunogen, or the host's production of antibodies against “self,” etc. However, these usually affect the lymphoid and other parts of the hematopoietic system, giving rise to toxic effects to the bone marrow (hematopoietic) and other normal host cells. Particularly in sepsis, where an immunosuppressed status is encountered, use of immunosuppressive therapies would be counter-indicated, so it is a goal to effect a careful balance between targeting and inhibiting key cells of the adaptive immune system while not depleting those involved with the host maintaining an active immune system.
A need exists for improved, more selective therapy of cancer and diverse immune diseases, including sepsis and septic shock, inflammation, atherosclerosis, cachexia, graft-versus-host, and other immune dysregulatory disorders.